Following surgical procedures performed on the cornea of the eye, e.g., cornea transplants, LASIK (laser-assisted in-situ keratomileusis), RK (radial keratotomy) or other refractive correction procedures, it is sometimes necessary for the post-operative patient to be fitted with rigid gas permeable (“RGP”) contact lenses to provide satisfactory vision, or to address other medical concerns. Unfortunately, RGP contact lenses often rest on the same area of the eye in which the post-operative sutures or scar tissue are present. Since the sutures or scar tissue may be very sensitive to touch, it can be very difficult to fit post-operative patients with conventional RGP contact lenses that do not irritate the traumatized tissue. In some cases, practitioners must re-fit the post-operative patient dozens of times before satisfactory lenses are found. In other cases, no satisfactory lens can be found, and the patient's vision needs remain unmet. A need therefore exists, for a contact lens that is relatively comfortable when worn over sutures or scar tissue in the eye of a post-operative patient.
For example, it has become standard practice for donor corneas intended for use in cornea transplants to be harvested in the form of uniformly sized, circular-shaped pieces approximately 8 mm in diameter, known as “buttons.” During the transplant procedure, a corresponding 8 mm circle is incised from the center of the patient's damaged cornea. The donor cornea “button” is then inlayed into the incised area and stitched around its periphery onto the remaining portion of the old cornea. Thus, the typical cornea transplant patient has a traumatized “surgical junction” area on their post-transplant eye(s) that is disposed in a generally circular pattern having a median diameter of about 8 mm. This surgical junction area is extremely sensitive to touch for some time after surgery, and may remain sensitive in some patients for an indefinite period. Unfortunately, most conventional RGP contact lenses have abrupt curvature junctions or other discontinuities in the annular region of approximately 8 mm in diameter, frequently making them uncomfortable for use by post-transplant patients. A need therefore further exists, for a RGP contact lens that has no abrupt curvature junctions or discontinuities in the annular region around 8 mm in diameter.
It is known that severe corneal astigmatism is frequently encountered in post-cornea transplant cases. Severe corneal astigmatism can also result from non-transplant causes such as disease, aging and hereditary factors. Regardless of the astigmatism's cause, the conventional literature teaches that using RGP contact lenses to successfully correct severe corneal astigmatism, i.e., where “severe” is usually characterized as corneal astigmatism in excess of 2.0 diopters (although sometimes characterized as corneal astigmatism in excess of 3.0 diopters), requires the use of so-called “bi-toric” lens prescriptions. Unlike standard lenses, which have a curvature prescription that is radially uniform (i.e., the same in all radial planes), bi-toric lenses have two different curvatures prescriptions, typically specified for roughly perpendicular radial planes. Although most practitioners can easily do the calculations required to fit a patient with a standard (i.e., radially uniform curvature) prescription, many practitioners find the calculations required to fit a patient with a bi-toric prescription to be prohibitively complex. In addition to being difficult to prescribe, bi-toric lenses are difficult to manufacture, resulting in a materially higher cost than standard lenses. This problem is further exacerbated if the practitioner must multiple fittings are required on the patient. A need therefore exists, for a RGP contact lens having a simple radially symmetrical curvature that can be used to treat severe corneal astigmatism in excess of 3.0 diopters.
It is further known that the precision of the refractive correction achievable using conventional rigid gas permeable (RGP) contact lenses is typically much better than that achievable using so-called “soft” contact lenses. Nonetheless, many patients choose to wear soft contact lenses because they are found to be more comfortable than conventional RGP lenses. It is believed that some of the comfort problems associated with conventional RGP contact lenses are the result of inadequate tear flow under the lens due to poor lens design. A need therefor exists, for a RGP contact lens design that provides improved tear flow under the lens, resulting in improved comfort to the wearer.